Since leaving the White House, Clinton has been thinner and seemingly healthier than he has been in decades as a result of a rigorous workout regime and a modified version of the South Beach diet, which limits carbohydrates and fats. His doctors said his ongoing treatment would include medication and a strict new diet.

Clinton has jogged regularly since college but has acknowledged to friends that he ran 3 to 5 miles a few times a week primarily so he could feel free to eat what he wanted. As a young man and well into his five terms as Arkansas governor, Clinton's eating exploits were legendary — including such feats as eating an entire pie at a single political event. At a famous 1994 lunch with German chancellor Helmut Kohl at an Italian restaurant in Washington, both men were estimated by White House reporters to have consumed more than 4,000 calories each.

The surgery marks the first real health crisis of Clinton's life. During his presidency, he had a benign cyst taken off his chest and a pre-cancerous lesion removed from his nose. Shortly after leaving office, he had a cancerous growth removed from his back. And in 1997, Clinton required surgery to repair a torn tendon in his right knee after stumbling on steps at the West Palm Beach, Fla., home of professional golf star Greg Norman.

Clinton's surgery also has had a political impact. He was expected to be a well-traveled surrogate for Kerry in the eight weeks that remain before the November election. While Clinton's negatives remain high among many swing and independent voters, party strategists felt he could help drive turnout among the party's base, among whom he remains hugely popular.

His doctors did not rule out that possibility. But they stressed that most patients need at least six weeks to be back to 70 percent of their pre-surgery energy level.

Former Clinton aides and longtime friends said they expected the always-impatient former president to be campaigning much earlier than his doctors expect.